Communication connection apparatus and communication system

ABSTRACT

A communication connection apparatus controls connection of a communication line between a first and second communication devices comprising: a first connection port for the first communication device, including a first transmission unit through which a signal from the first communication device passes and a first reception unit through which a signal for the first communication device passes; a second connection port for the second communication device, including a second transmission unit through which a signal from the second communication device passes and a second reception unit through which a signal for the second communication device passes; a first connection line connecting the first transmission unit and the second reception unit; and a simulated-signal input unit that inputs a first signal to the first reception unit. On the first signal being input to the first reception unit, the first reception unit and the second transmission unit are physically disconnected.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a national stage of PCT International ApplicationNo. PCT/JP2016/065417, filed on May 25, 2016, which claims priority toand incorporates by reference the entire contents of Japanese PatentApplication No. 2015-110627 filed in Japan on May 29, 2015.

The present disclosure relates to a communication connection apparatusand a communication system including the same.

BACKGROUND

With regard to a control device used in power generation facilities anddisaster-prevention infrastructure facilities such as gates andfloodgates of a dam, high security characteristics enabling preventionof illegal access and virus entry from outside are required. Meanwhile,in order to achieve operability improvement and quick response in caseof trouble, there are cases where acquisition of information from adevice, for which high security characteristics are required, via acommunication network is required. When such a communication system isestablished, various types of devices are provided to protect a devicefor which high security characteristics are required.

For example, there is described a communication system including: a datacollection device that is connected to disaster-preventioninfrastructure facilities and collects facility data related to thedisaster-prevention infrastructure facilities; an intermediate storagedevice that is provided separately from the data collection device andincludes an intermediate storage unit that stores therein facility datacollected by the data collection device; a remote monitoring device thatcan receive the facility data stored in the intermediate storage unit ofthe intermediate storage device via an external network; and a switchdevice that can switch a state of the communication system among adisconnection state in which communication between the data collectiondevice and the intermediate storage device is disconnected andcommunication between the intermediate storage device and the externalnetwork is disconnected, a first connection state in which the datacollection device and the intermediate storage device are connected toeach other to be at least capable of communicating the facility data andthe communication between the intermediate storage device and theexternal network is disconnected, and a second connection state in whichthe communication between the data collection device and theintermediate storage device is disconnected and the intermediate storagedevice and the external network are connected to each other to be atleast capable of communicating the facility data (Japanese Laid-openPatent Publication No. 2013-195398).

Even when the communication system described in Japanese Laid-openPatent Publication No. 2013-195398 is used, the system can be set in astate of being physically connected to a communication line, and thusthere is a risk that a protection-target communication device becomesaccessible. Further, by connecting two communication devicescommunicating with each other via a dedicated line, it is possible toimprove the security of these devices; however, if the two devicescommunicating with each other are provided to be apart, installation ofthe dedicated line is troublesome.

An object of the invention is to provide a communication connectionapparatus that can output data from a protection-target communicationdevice to another communication device with a simple configuration whilepreventing access to the protection-target communication device, and acommunication system including the communication connection apparatus.

According to the present disclosure, there is provided a communicationconnection apparatus that is configured to control connection of acommunication line between at least one first communication device andat least one second communication device, the communication connectionapparatus comprising: a first connection port to which a connection lineto the at least one first communication device is connected, and whichincludes a first transmission unit through which a signal output fromthe at least one first communication device passes and a first receptionunit through which a signal to be input to the at least one firstcommunication device passes; a second connection port to which aconnection line to the at least one second communication device isconnected, and which includes a second transmission unit through which asignal output from the at least one second communication device passesand a second reception unit through which a signal to be input to the atleast one second communication device passes; a first connection linethat connects the first transmission unit and the second reception unitto each other; and a simulated-signal input unit that inputs, to thefirst reception unit, a first signal which is a signal for recognizingthat the at least one first communication device is connectable to otherdevices, wherein when the first signal is being input to the firstreception unit, the first reception unit and the second transmissionunit are physically disconnected from each other.

The above and other objects, features, advantages and technical andindustrial significance of this disclosure will be better understood byreading the following detailed description of presently preferredembodiments of the disclosure, when considered in connection with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a schematic configuration of acommunication system.

FIG. 2 is a front view illustrating an exterior of a communicationconnection apparatus.

FIG. 3 is a block diagram illustrating a schematic configuration of thecommunication connection apparatus.

FIG. 4 is an explanatory diagram for explaining an operation of thecommunication connection apparatus.

FIG. 5 is an explanatory diagram for explaining an operation of thecommunication connection apparatus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

An exemplary embodiment of the present disclosure will be describedbelow with reference to accompanying drawings. The present disclosure isnot limited to this embodiment. Constituent elements described in thefollowing embodiment include elements that are easily replaceable bypersons skilled in the art and elements that are substantiallyequivalent.

FIG. 1 is a block diagram illustrating a schematic configuration of acommunication system. In a communication system 10, a communicationdevice provided in an upstream facility 12 and a communication deviceprovided in a downstream facility 16 are connected to each other via anInternet communication network 14. In this example, the communicationdevices are various types of devices that can perform transmission andreception of data. The upstream facility 12 is a facility in which aprotection-target communication device is provided. As the upstreamfacility 12, power generation facilities and disaster-preventioninfrastructure facilities such as gates and floodgates of a dam can beexemplified. The Internet communication network 14 is a publiccommunication network, and connects communication between communicationdevices that are connected to the communication network in a wired orwireless manner, for example. The downstream facility 16 is a facilitythat receives information from the communication device of the upstreamfacility 12 and performs remote monitoring. The downstream facility 16includes a router 20 and a terminal (second communication device,downstream communication device) 22. The terminal 22 is a personalcomputer, for example. The terminal 22 is connected to the Internetcommunication network 14 via the router 20. The terminal 22 performscommunication with another communication device that is connectedthereto via the Internet communication network 14 and performstransmission and reception of data.

The upstream facility 12 includes first communication devices (upstreamcommunication devices) 30, a hub 32, a communication connectionapparatus 34, a router 36, and a power source 38. The firstcommunication devices (upstream communication devices) 30 include aplurality of devices that are provided in the upstream facility 12 andhave a function of transmitting and receiving data. In FIG. 1, a controldevice 30 a, a PLC (Programmable Logic Controller) 30 b, and a terminal30 c are provided as the first communication devices 30. The firstcommunication devices 30 are not limited to the devices described above,and other various communication devices can be used. For example, as thefirst communication device 30, a workstation or a data server can beused. Further, it suffices that the first communication device 30 isconstituted by at least one device, and the configuration thereof is notparticularly limited to any specific one. The first communicationdevices 30 can accumulate data such as measurement data and controlconditions of an operating target of the upstream facility 12 and canoutput the accumulated data.

The hub 32 is provided between the plurality of first communicationdevices 30 and the communication connection apparatus 34. The hub 32integrates lines of the plurality of first communication devices 30 toconnect each of the plurality of first communication devices 30 and thecommunication connection apparatus 34 to each other. The communicationconnection apparatus 34 is described later. The router 36 connects thecommunication connection apparatus 34 and the Internet communicationnetwork 14 to each other. The power source 38 is a supply source forsupplying power to the communication connection apparatus 34.

Next, with reference to FIGS. 2 and 3 along with FIG. 1, details of thecommunication connection apparatus 34 are described. FIG. 2 is a frontview illustrating an exterior of the communication connection apparatus.FIG. 3 is a block diagram illustrating a schematic configuration of thecommunication connection apparatus. The communication connectionapparatus 34 is connected to the hub 32 and the router 36. Therefore,the communication system 10 connects the first communication devices 30and the terminal (second communication device) 22 to each other via thehub 32, the communication connection apparatus 34, the router 36, theInternet communication network 14, and the router 20.

The communication connection apparatus 34 establishes a communicationstate (a first communication mode) in which data can be output from thefirst communication devices 30 to the terminal (second communicationdevice) 22, and access to the first communication devices 30 fromdevices which include the terminal (second communication device) 22 andare provided on the side of the router 36 with respect to thecommunication connection apparatus 34 cannot be made. Further, thecommunication connection apparatus 34 according to the presentembodiment can switch the state of the communication system 10 to astate (a second communication mode) in which data communication can beperformed bidirectionally between the first communication devices 30 andthe terminal (second communication device) 22.

As illustrated in FIGS. 1 and 2, the communication connection apparatus34 includes a first connection port (upstream port) 42, a secondconnection port (downstream port) 44, a physical switch 46, a displayunit 48, and a power-source physical switch 49. The first connectionport 42 is a connection unit that is connected to the hub 32 via acommunication line (data line). The second connection port 44 is aconnection unit that is connected to the router 36 via a communicationline (data line).

The physical switch 46 is a switch that is operated by a user to switchbetween the first communication mode and the second communication mode.The physical switch 46 includes a keyhole 46 a and a key 46 b that isinsertable to the keyhole 46 a. With regard to the physical switch 46,an orientation of the keyhole 46 a is changed according to a directionof the key 46 b. The physical switch 46 switches between the firstcommunication mode and the second communication mode according to theorientation of the keyhole 46 a.

The display unit 48 includes a unidirectional communication display lamp48 a and a bidirectional communication display lamp 48 b. On the displayunit 48, when the communication system 10 is in the first communicationmode, the unidirectional communication display lamp 48 a is turned onand the bidirectional communication display lamp 48 b is turned off. Onthe display unit 48, when the communication system 10 is in the secondcommunication mode, the unidirectional communication display lamp 48 ais turned off and the bidirectional communication display lamp 48 b isturned on. The power-source physical switch 49 is a switch by which auser inputs an operation for switching ON and OFF of power supply fromthe power source 38 to the communication connection apparatus 34.

Next, functional configurations of the communication connectionapparatus 34 are described. As illustrated in FIG. 3, the communicationconnection apparatus 34 includes a switching unit 47, a simulated-signalinput unit 50, a power-source circuit switch 52, a control device 54, afirst connection line 60, and second connection lines 62, 64, and 66 (aline unit), in addition to the first connection port 42, the secondconnection port 44, the physical switch 46, the display unit 48, and thepower-source physical switch 49.

The first connection port 42 is connected to the hub 32 via thecommunication line, and includes a first transmission unit 42 a and afirst reception unit 42 b. Signals output from the first communicationdevices 30 pass through the first transmission unit 42 a via the hub 32.That is, data transmitted from the first communication devices 30 passesthrough the first transmission unit 42 a. Signals to be input to thefirst communication devices 30 pass through the first reception unit 42b via the hub 32. That is, data to be received by the firstcommunication devices 30 passes through the first reception unit 42 b.

The second connection port 44 is connected to the router 36 via thecommunication line, and includes a second transmission unit 44 a and asecond reception unit 44 b. Signals output from the terminal 22 passthrough the second transmission unit 44 a via the router 36, theInternet communication network 14, and the like. That is, datatransmitted from the terminal 22 passes through the second transmissionunit 44 a. Signals to be input to the terminal 22 via the router 36, theInternet communication network 14, and the like pass through the secondreception unit 44 b. That is, data to be received by the terminal 22passes through the second reception unit 44 b. The first connection line60 connects the first transmission unit 42 a and the second receptionunit 44 b to each other.

The switching unit 47 switches between the first communication mode andthe second communication mode in conjunction with operations on thephysical switch 46. The switching unit 47 includes a movable unit 47 a,a terminal 47 b, and a terminal 47 c. The movable unit 47 a is connectedto the second connection line 62. The terminal 47 b is connected to thesecond connection line (line unit) 66. The terminal 47 c is connected tothe second connection line 64. The second connection line 62 connectsthe first reception unit 42 b and the switching unit 47 to each other.The second connection line 64 connects the second transmission unit 44 aand the switching unit 47 to each other. The second connection line 66connects the simulated-signal input unit 50 and the switching unit 47 toeach other. By connecting the movable unit 47 a and the terminal 47 b toeach other, the switching unit 47 sets a state in which the firstreception unit 42 b and the simulated-signal input unit 50 are connectedto each other, thereby realizing the first communication mode. Byconnecting the movable unit 47 a and the terminal 47 c to each other,the switching unit 47 sets a state in which the first reception unit 42b and the second transmission unit 44 a are connected to each other,thereby realizing the second communication mode.

The simulated-signal input unit (first signal input unit) 50 outputs asimulated signal (first signal). When the switching unit 47 is in thefirst communication mode, the simulated signal output from thesimulated-signal input unit 50 passes through the first reception unit42 b and is input to the first communication devices 30. The simulatedsignal is a signal for the first communication devices 30 to recognizethat they are in a state of outputting a signal, that is, for the firstcommunication devices 30 to recognize that communication with othercommunication devices has been established. In other words, thesimulated signal is a signal for recognizing that the firstcommunication devices 30 are connectable to other devices.

The simulated-signal input unit 50 includes two internal communicationdevices (serial Ethernet converters) 70 and 72. The two internalcommunication devices 70 and 72 have an identical configuration. Theinternal communication device 70 includes a serial port 74 a and anEthernet® port 76 a. The serial port 74 a receives a seizing signalinput from the control device 54. Upon reception of the seizing signal,the serial port 74 a outputs a command for starting a communicationestablishing operation to the Ethernet° port 76 a. The Ethernet® port 76a includes a transmission unit 78 a and a reception unit 79 a.

The internal communication device 72 includes a serial port 74 b and anEthernet° port 76 b. The serial port 74 b receives a seizing signalinput from the control device 54. Upon reception of the seizing signal,the serial port 74 b outputs a command for starting a communicationestablishing operation to the Ethernet° port 76 b. The Ethernet° port 76b includes a transmission unit 78 b and a reception unit 79 b. In thesimulated-signal input unit 50, the Ethernet° port 76 a and theEthernet° port 76 b are connected to each other via a communicationline. Specifically, in the simulated-signal input unit 50, thetransmission unit 78 a of the Ethernet° port 76 a and the reception unit79 b of the Ethernet° port 76 b are connected to each other. Further, inthe simulated-signal input unit 50, the transmission unit 78 b of theEthernet° port 76 b and the reception unit 79 a of the Ethernet° port 76a are connected to each other.

When the simulated-signal input unit 50 is activated, a seizing signalis input from the control device 54 to both serial ports 74 a and 74 bof the internal communication devices 70 and 72, respectively. In thesimulated-signal input unit 50, when a seizing signal is input to theserial ports 74 a and 74 b, communication is established between theEthernet° port 76 a and the Ethernet® port 76 b.

In the simulated-signal input unit 50, a line connecting thetransmission unit 78 a and the reception unit 79 b to each other isconnected to the second connection line 66. The simulated-signal inputunit 50 outputs, as a simulated signal, a signal indicating thatcommunication of a signal transmitted from the transmission unit 78 a tothe reception unit 79 b is established to the second connection line 66.

The power-source circuit switch 52 is provided on a power line thatconnects the power source 38 and the control device 54 to each other.The power-source circuit switch 52 switches, in conjunction with thepower-source physical switch 49, ON and OFF of the connection betweenthe power source 38 and the control device 54. The power supplied to thecontrol device 54 is transmitted to respective units of thecommunication connection apparatus 34 via the control device 54.

The control device 54 controls activating and deactivating of thesimulated-signal input unit 50, and controls a lighting state of thedisplay unit 48 according to the state of the switching unit 47. Itsuffices that the control device 54 is a control circuit that outputs aset signal based on an input signal.

Next, with reference to FIGS. 4 and 5, operations of the communicationconnection apparatus are described. FIGS. 4 and 5 are explanatorydiagrams for explaining operations of the communication connectionapparatus. FIG. 4 illustrates a state of the first communication mode.FIG. 5 illustrates a state of the second communication mode.

As illustrated in FIG. 4, when the movable unit 47 a of the switchingunit 47 is connected to the terminal 47 b according to the operation onthe physical switch 46, the communication connection apparatus 34performs communication in the first communication mode. In this case, inthe communication connection apparatus 34, the unidirectionalcommunication display lamp 48 a is turned on and the bidirectionalcommunication display lamp 48 b is turned off.

In the communication connection apparatus 34, as the movable unit 47 aof the switching unit 47 is connected to the terminal 47 b, thesimulated-signal input unit 50 and the first reception unit 42 b areconnected to each other, and the second transmission unit 44 a and thefirst reception unit 42 b are disconnected from each other. Due to thisconfiguration, in the communication connection apparatus 34, a simulatedsignal output from the simulated-signal input unit 50 is input to thefirst reception unit 42 b. In the communication system 10, the simulatedsignal output from the simulated-signal input unit 50 passes through thefirst reception unit 42 b, and is input to the first communicationdevices 30. Upon input of the simulated signal, the first communicationdevices 30 determine that communication with other devices has beenestablished, and output set data. In this case, the first communicationdevices 30 are set to output data in UDP (User Datagram Protocol)broadcast communication. The data output from the first communicationdevices 30 passes through the first transmission unit 42 a, the firstconnection line 60, and the second reception unit 44 b, and is output tothe router 36 from the communication connection apparatus 34. The dataoutput to the router 36 is output to the Internet communication network14. The terminal (second communication device) 22 receives the dataoutput to the Internet communication network 14, thereby receiving thedata output from the first communication devices 30.

Next, as illustrated in FIG. 5, when the movable unit 47 a of theswitching unit 47 is connected to the terminal 47 c according to theoperation on the physical switch 46, the communication connectionapparatus 34 performs communication in the second communication mode. Inthis case, in the communication connection apparatus 34, theunidirectional communication display lamp 48 a is turned off and thebidirectional communication display lamp 48 b is turned on.

In the communication connection apparatus 34, as the movable unit 47 aof the switching unit 47 is connected to the terminal 47 c, the secondtransmission unit 44 a and the first reception unit 42 b are connectedto each other. In the communication connection apparatus 34, thetransmission unit and the reception unit in both directions between thefirst communication devices 30 and the terminal 22 are connected to eachother respectively, so that bidirectional communication between thefirst communication devices 30 and the terminal 22 can be performed. Inthe communication connection apparatus 34, a signal for establishingcommunication output from the terminal 22 is input to the firstcommunication devices 30 via the second transmission unit 44 a, thefirst reception unit 42 b, and the like. Further, in the communicationconnection apparatus 34, a signal for establishing communication outputfrom the first communication device 30 is input to the terminal 22 viathe first transmission unit 42 a, the second reception unit 44 b, andthe like. In this manner, in the communication system 10 in the secondcommunication mode, communication is established between the firstcommunication devices 30 and the terminal 22 in bidirectionalcommunication, thereby realizing a state in which data can betransmitted and received between the first communication devices 30 andthe terminal 22. In this case, between the first communication devices30 and the terminal 22, mutual authentication is made by using, forexample, a TCP (Transmission Control Protocol)/IP (Internet Protocol)protocol to establish communication.

Due to the configuration described above, when the communicationconnection apparatus 34 is in the first communication mode, a simulatedsignal is input to the first communication devices 30 via the firstreception unit 42 b and the first communication devices 30 are caused todetermine that communication is established, so that data can be outputfrom the first communication devices 30 in a state in which the firstreception unit 42 b and the second transmission unit 44 a are physicallydisconnected from each other. Due to this configuration, it is possibleto set a state in which a line for transmitting data to the firstcommunication devices 30 from communication devices on a downstream side(the side of the router 36) with respect to the communication connectionapparatus 34 is physically disconnected. Due to this configuration, itis possible to set a state in which the first communication devices 30cannot be physically accessed from the downstream side (the side of therouter 36) with respect to the communication connection apparatus 34,and it is possible to prevent illegal access and virus entry to thefirst communication devices 30, thereby setting the first communicationdevices 30 to be in a safer state.

Further, in the communication system 10, by setting the firstcommunication devices 30 to output data in UDP (User Datagram Protocol)broadcast communication, output of data from the first communicationdevices 30 can be started with input of a simulated signal that is asignal indicating establishment of communication between othercommunication devices.

Further, when the first communication devices 30 output data, it ispreferable that the data is partitioned in accordance with an outputformat of the data, specifically, partitioned in accordance with apacket of UDP broadcast communication, and that each piece of data istransmitted with an identification (ID) code attached thereto. In thiscase, by combining received pieces of data based on their identification(ID) codes, the terminal 22 can reproduce the original data. Due to thisconfiguration, data having a large data amount can be transmitted.Further, even if data is defective, the data can be recognized based onits identification (ID) code.

When power supply from the power source 38 is stopped, the communicationconnection apparatus 34 stops output of a simulated signal. Due to thisconfiguration, when the communication connection apparatus 34 has afailure in the first communication mode, input of a simulated signal tothe first communication devices 30 is stopped while a state ismaintained in which a line from other communication devices to the firstcommunication devices 30 via the communication connection apparatus 34is not connected. Due to this configuration, it is possible to maintaina state in which access to the first communication devices 30 from othercommunication devices on the downstream side with respect to thecommunication connection apparatus 34 cannot be made, therebymaintaining the safety of the first communication devices 30.

In the communication connection apparatus 34, by providing the physicalswitch 46 and the switching unit 47 and also providing a route that canconnect the first reception unit 42 b and the second transmission unit44 a to each other, it is possible to make the first communication modeand the second communication mode selectable.

It is preferable that the communication connection apparatus 34 has aconfiguration such that, in a state in which the key 46 b of thephysical switch 46 is inserted into the keyhole 46 a, the key 46 b isoriented to a predetermined direction, and the key cannot be removedfrom the keyhole 46 a, the mode of the communication connectionapparatus 34 is switched to the second communication mode. Due to thisconfiguration, only when the key 46 b is inserted into the keyhole 46 aand set in a predetermined orientation, communication in the secondcommunication mode can be performed.

The technical scope of the present invention is not limited to theembodiment described above, and modifications can be made as appropriatewithout departing from the scope of the present invention.

In the communication connection apparatus 34 according to the embodimentdescribed above, while the switching unit 47 is provided and the firstcommunication mode and the second communication mode are switchable, itis also possible to configure the communication connection apparatus 34in which only the first communication mode is executable. In thismanner, by having a configuration in which the second communication modecannot be executed, it is possible to more securely set a state in whichdata cannot be transmitted to the first communication devices 30 fromthe side of the router 36 (the downstream side) with respect to thecommunication connection apparatus 34, and it is also possible toprevent access from outside to the first communication devices 30 moresecurely.

In the communication connection apparatus 34 according to the embodimentdescribed above, the simulated-signal input unit 50 includes the twointernal communication devices 70 and 72, and a signal indicatingestablishment of communication between the two internal communicationdevices 70 and 72 is input to the first reception unit 42 b, for havinga high possibility of the first communication devices 30 determiningthat communication is established and for outputting data from the firstcommunication devices 30 more easily; however, the simulated signal tobe input to the first reception unit 42 b is not limited thereto. Itsuffices that the simulated signal is a signal by which it is possiblefor the first communication devices 30 to determine that communicationis established. For example, it is possible to have a configuration suchthat the simulated-signal input unit 50 uses an oscillator thatgenerates the same signal as the signal by which it is possible for thefirst communication devices 30 to determine that communication isestablished, and such that a signal output from the oscillator isregarded as a simulated signal.

It is preferable that the simulated-signal input unit 50 outputs data ofa serial signal. By setting the signal as a serial signal, the simulatedsignal is more recognizable. Further, the simulated-signal input unit 50can also output a signal of text data in addition to a simulated signal.Due to this configuration, by outputting a signal of text data from thesimulated-signal input unit 50, processing in the first communicationdevices 30 can be performed more easily, and a signal output from thesimulated-signal input unit 50 can be used more easily for controllingconfirmation of the communication state.

In the embodiment described above, a case where a general communicationline is used as the Internet communication network 14 has beenexemplified; however, the embodiment is not limited thereto. Forexample, it is possible to employ a configuration in which a dedicatedline and a general communication line are used together as thecommunication network.

According to the present disclosure, it is possible to configure so thatoutput of data from a second communication device to a firstcommunication device with physical connection cannot be made, and thatoutput of data from the first communication device to the secondcommunication device can be made. Due to this configuration, data can beoutput from a protection-target communication device to anothercommunication device with a simple configuration while access to theprotection-target communication device is prevented.

Although this disclosure has been described with respect to specificembodiments for a complete and clear disclosure, the appended claims arenot to be thus limited but are to be construed as embodying allmodifications and alternative constructions that may occur to oneskilled in the art that fairly fall within the basic teaching herein setforth.

1. A communication connection apparatus that is configured to controlconnection of a communication line between at least one firstcommunication device and at least one second communication device, thecommunication connection apparatus comprising: a first connection portto which a connection line to the at least one first communicationdevice is connected, and which includes a first transmission unitthrough which a signal output from the at least one first communicationdevice passes and a first reception unit through which a signal to beinput to the at least one first communication device passes; a secondconnection port to which a connection line to the at least one secondcommunication device is connected, and which includes a secondtransmission unit through which a signal output from the at least onesecond communication device passes and a second reception unit throughwhich a signal to be input to the at least one second communicationdevice passes; a first connection line that connects the firsttransmission unit and the second reception unit to each other; and asimulated-signal input unit that inputs, to the first reception unit, afirst signal which is a signal for recognizing that the at least onefirst communication device is connectable to other devices, wherein whenthe first signal is being input to the first reception unit, the firstreception unit and the second transmission unit are physicallydisconnected from each other.
 2. The communication connection apparatusaccording to claim 1, wherein the first signal is a serial signal. 3.The communication connection apparatus according to claim 2, wherein thesimulated-signal input unit includes two internal communication devicesand a line unit that is connected to the first reception unit, and thesimulated-signal input unit causes communication between the twointernal communication devices to be established, and inputs a signaloutput from a transmission unit of either one of the two internalcommunication devices to a reception unit of the other one of the twointernal communication devices to the first reception unit via the lineunit as the first signal.
 4. The communication connection apparatusaccording to claim 1, comprising: a switching unit that is provided on aline connecting the simulated-signal input unit and the first receptionunit to each other; and a second connection line that connects theswitching unit and the second transmission unit to each other, whereinthe switching unit switches a state of the communication connectionapparatus between a state in which the simulated-signal input unit andthe first reception unit are connected to each other and a state inwhich the second connection line and the first reception unit areconnected to each other.
 5. The communication connection apparatusaccording to claim 4, comprising a physical switch that switches aconnection state of the switching unit, wherein the physical switchincludes a key and a keyhole, and the second connection line and thefirst reception unit can be connected to each other only in a state inwhich the key is inserted into the keyhole.
 6. The communicationconnection apparatus according to claim 1, wherein the first signal is asignal for recognizing that data can be output from the firsttransmission unit in UDP broadcast communication.
 7. A communicationsystem comprising: at least one first communication device; at least onesecond communication device; the communication connection apparatusaccording to claim 1; and a public communication line network thatconnects the at least one second communication device and thecommunication connection apparatus to each other.